Hot Probe Research Articles

A new route for the synthesis of n-type Ag2ZnSnS4 thin films by thermal vacuum evaporation for solar cell applications

Special interest has been recently devoted to the quaternary material Ag2ZnSnS4 (AZTS) due to its remarkable electrical and optical properties. Our study proposes a new method for the synthesis of Ag2ZnSnS4 thin films by thermal vacuum evaporation on soda-lime glass (SLG) substrates by tuning their thickness. Structural characterization of thin films, performed by X-ray diffraction and Raman spectroscopy, confirmed the presence of the AZTS stannite phase with the appearance of the Ag8SnS6 secondary phase. As the thickness increases, a transition from amorphous to polycrystalline state appears in the XRD spectra, along with an increase in intensity related to a refinement of the preferential peak (112), an increase in crystallite size and a decrease in stress and dislocations. Compositional analysis confirms the stoichiometric composition of the films. Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM) reveal a strong thickness dependence of the film on the surface structure. Moreover, the thickness affects significantly the optical properties of films. In particular, an increase of the absorption coefficients associated with a decrease of the direct gap energy and the Urbach energy is observed with increasing thickness. The optical and dielectric constants have been studied and discussed in more detail based on the single oscillator model proposed by Wemple DiDomenico and other models. The static refractive indices as well as the static dielectric constant of the layers show a slight increase with layer thickness, in contrast to the oscillator energy. Finally, all samples display n-type conductivity according to the hot probe experiment. Such attractive characteristics can be useful to further improve the efficiency of thin film solar cells by adjusting the thin film thickness.

Growth of Cu2ZnSnS4 Thin Film Solar Cells Using Chemical Synthesis

Objectives: Cu2ZnSnS4 thin film solar cell is fabricated by using the chemical spray pyrolysis method. Method: CZTS thin films were successfully deposited by employing the eco-friendly and cost-effective chemical spray pyrolysis method. X-ray diffraction (XRD) and Raman spectroscopy are used to investigate the structural properties of the prepared samples. The surface morphology of the deposited films is studied using a scanning electron microscope. An energy dispersive spectrometer is used to know the chemical compositions of the deposited films. A double beam spectrophotometer is used to study the optical characteristics of these films. The hot probe technique is used to confirm the nature of the conductivity of the deposited films. Findings: The XRD spectra of the thin films reveal the polycrystalline nature with the kesterite structure of the thin films. The optical band gap is found to be 1.52 eV and the absorption coefficient value of these films is found to be  104 cm-1. The nature of conductivity is identified to be p-type. Finally, Cu2ZnSnS4 thin film solar cell is fabricated with the substrate configuration glass/Mo/CZTS/CdS/Ag which exhibited an open circuit voltage and short circuit current of 156 mV and 1.82 mA/cm2 respectively. Novelty: The growth of Cu2ZnSnS4 thin films is studied by varying the distance between the spray nozzle and glass substrate from 25 to 35 cm in steps of 5 cm and maintaining all other parameters as constant. Finally, the Cu2ZnSnS4 thin film solar cell is prepared in a substrate as well as a superstrate configuration. Keywords: Thin films; Absorber layers; Spray technique; Solar cell; Cu2ZnSnS4

Synthesis and Characterization of High-Efficiency Halide Perovskite Nanomaterials for Light-Absorbing Applications.

Inorganic perovskite materials are possible candidates for conversion of solar energy to electrical energy due to their high absorption coefficient. Perovskite solar cells (PSCs) introduced a new type of device structure that has attention due to better efficiencies and interest in PSCs that has been increasing in recent years. Halide perovskite materials such as CsPbIBr2 show remarkable optical and structural performance with their better physical properties. Perovskite solar cells are a possible candidate to replace conventional silicon solar panels. In the present study, CsPbIBr2 perovskite materials' thin films were prepared for light-absorbing application. Five thin films were deposited on the glass substrates by subsequent spin-coating of CsI and PbBr2 solutions, subsequently annealed at different temperature values (as-deposited, 100, 150, 200 and 250 °C) to get CsPbIBr2 thin films with a better crystal structure. Structural characterizations were made by using X-ray diffraction. CsPbIBr2 thin films were found to be polycrystalline in nature. With increasing annealing temperature, the crystallinity was improved, and the crystalline size was increased. Optical properties were studied by using transmission data, and by increasing annealing temperature, a small variation in optical band gap energy was observed in the range of 1.70-1.83 eV. The conductivity of CsPbIBr2 thin films was determined by a hot probe technique and was found to have little fluctuating response toward p-type conductivity, which may be due to intrinsic defects or presence of CsI phase, but a stable intrinsic nature was observed. The obtained physical properties of CsPbIBr2 thin films suggest them as a suitable candidate as a light-harvesting layer. These thin films could be an especially good partner with Si or other lower band gap energy materials in tandem solar cells (TSC). CsPbIBr2 material will harvest light having energy of ∼1.7 eV or higher, while a lower energy part of the solar spectrum will be absorbed in the partner part of the TSC.

Comparative studies of cold/hot probe techniques for accurate plasma measurements

The emissive probe technique and the cold Langmuir probe technique for the plasma potential measurement are compared in microwave electron cyclotron resonance plasmas. With different results of plasma potential, discrepant results of electron temperature and electron density are obtained from a hot emissive probe I–V curve and a cold Langmuir probe I–V curve, respectively. A comparison of the experimental data shows that the plasma parameters obtained from the cold Langmuir probe I–V curve are always grossly underestimated, while the results determined from the hot emissive probe I–V curve are much more reliable. Additionally, based on the experimental results, a novel emissive probe technique named the hot probe with zero emission limit method is proposed to easily obtain the accurate plasma potential and other reliable plasma parameters.

Nano-crystalline tin selenide thin films: synthesis and characterization

A simple, straightforward, and facile drop-casting technique was used to prepare thin films of tin selenide (SnSe) at 220 °C substrate temperature using triethanolamine as complexing agent. SnCl2 and Na2SeSO3 precursors were used as source materials for the thin film synthesis. The drop-casted film was annealed at 400 °C. Surface morphological, structural, electrical, and optical properties of the synthesized films were analyzed by scanning electron microscope (SEM), energy dispersive X-ray analysis (EDAX), X-ray powder diffraction (XRD), high-precision digital multimeter, and UV–visible spectroscopy, respectively. The XRD study of synthesized film showed the presence of nanocrystallinity with orthorhombic crystal structure of SnSe. SEM images indicated that small grains agglomerated to form a bunch of bigger size. SEM data showed good continuity of SnSe film. Hot probe method was used to confirm the carrier type of film. SnSe thin films were p-type having 1.4 eV bandgap, and their electrical conductivity was in the order of 10 S cm−1 which made them suitable to use it in the solar cell as an absorber layer.

Growth and characterization of stochiometric PbxZn1-xS (x = 0.5) thin films by spray pyrolysis for solar cell window applications

Mixed II-IV-VI compounds are important because of the possibility of band gap tuning. Attempts have been made to grow polycrystalline PbxZn1-xS (x = 0.5) thin films by the spray pyrolysis technique. Films have been grown on glass substrates at substrate temperature 400 °C. X-ray diffractometer studies reveals that the films are cubic in nature with a preferred orientation along (111) texture. By the EDAX analysis the Stoichiometry of the deposited films was confirmed. SEM photographs show that the films were smooth and homogeneous. The transmittance measurements in the UV– VIS wavelength range show the optical band gap of 2.11 eV. Hot probe method reveals that films exhibit n type conductivity. The measurement of resistance with temperature revealed the extrinsic activation energy of 0.28 eV.

Structural, morphology and optical properties of PbS (Lead Sulfide) thin film

We report here the synthesis, structural and optical properties of PbS thin film. The growth rate in the chemical path deposition time was optimized during film deposition. The surface of the PbS film is compact and well covered, with a smooth surface and irregularly shaped spherical grain of random sizes. The electrical studies were measure with the Hall effect and Hot probe for the optimized film and the transmittance and band gap of the films were measure by the UV–VIS–NIR Spectrometer in the range of 400–2500 nm. It was observed that the band gap decreases and thickness increased with the increases in deposition time. The room temperature photoluminescence emission spectra of the as grown PbS thin films. Radiation of wavelength 425 nm was used for excitation.

Pyrite as prospective absorber material for monograin layer solar cell

FeS2 monograin powders as absorber materials in monograin layer solar cells were grown in the molten phase of two different flux materials - in liquid sulphur (S) and in potassium iodide (KI) at different temperatures - at 500 °C, 550 °C, 600 °C in S and at 740 °C in KI. The cooling temperature profiles were modified to preserve the pyrite phase of material until room temperature was reached. FeS2 microcrystals, synthesized in sulphur and recrystallized in molten KI as flux, had cubic structure of pyrite phase with stoichiometric composition, confirmed by X-ray diffraction, Raman, and energy dispersive X-ray analyses, respectively. The grown FeS2 crystals exhibited n-type conductivity determined by hot probe measurements. The powder crystals were fixed in monograin membranes for making heterostructures with p-type nickel oxide (NiO) buffer layer. Charge carrier concentrations 6.2 × 1016 and 2.5 × 1017 cm−3, were found from capacitance-voltage measurements using FeS2/NiO heterostructures and FeS2/Pt Schottky diodes, respectively.

Extrinsic thermoelectric response of coherent conductors

We investigate the thermoelectric response of a coherent conductor in contact with a scanning probe. Coupling to the probe has the dual effect of allowing for the controlled local injection of heat currents into the system and of inducing interference patterns in the transport coefficients. This is sufficient to generate a multiterminal thermoelectric effect even if the conductor does not effectively break electron-hole symmetry and the tip injects no charge. Considering a simple model for noninteracting electrons, we find a nonlocal thermoelectric response which is modulated by the position of the hot probe tip, and a nonreciprocal longitudinal response which leads to a thermoelectric diode effect. A separate investigation of the effects of dephasing and of quasielastic scattering gives further insights into the different mechanisms involved.

Hot-Probe Method for Majority Charge Carrier Determination in Methylammonium Lead Halide Perovskites

Perovskites, due to their promising capabilities, are among the major candidates to substitute early-generation silicon solar cells. Despite their outstanding electrical and optical properties, actual comprehension of their behavior requires further studies and also investigation tools. It is shown that vacancy traps in organic-inorganic perovskites induce different polarities, where lead and methylamine vacancies posses p- and n-type polarity, respectively. Referred to as the self-doping property, different molar ratios of chemical precursors lead to controllable polarity and intrinsic doping. In other reports, thermal annihilation is also shown to convert p-type perovskite to n-type. According to the broad range of synthesized perovskites and their current application and promising future in optoelectronic devices, a simple, quick, and dependable method for trap concentration and major carrier-type determination is essential. Hot probe is a simple, affordable, and fast method for extracting polarity type in bulk and thin-film semiconductors. So far, this method and its variations have been applied for measuring conductivity, polarity, and impurity concentration in diverse ranges of semiconductors. In this method, free carriers are generated by raising the temperature of hot-probe contact and induced diffusion from this contact toward the other cold contact is studied. An equilibrium state is reached as a result of the formed built-in electric field between the cold and hot electrodes and also temperature elevation of this cold electrode, which act as diffusion dampers. Here, different types of organic-inorganic perovskites are synthesized and their electrical behavior is evaluated by the hot-probe method. Finally, it is concluded that the hot-probe approach is a dependable, fast, and accurate method to be applied in the field of perovskite material evaluations.

Synthesis, Growth and Characterization of Cu2CoSnS4 Thin Films via Thermal Evaporation Method

Quaternary sulfide Cu2CoSnS4 (CCTS) thin films were deposited by vacuum thermal evaporation on heated substrates. The substrates temperatures are ranged from room temperature to 200 °C. After what, the as-deposited films were sulfurized under vacuum at 450 °C to optimize the stoechiometric stannite CCTS phase. The crystalline structure of the sulfurized CCTS thin films was examined by X-ray diffraction technique and Raman spectroscopy. Surface morphological, elemental compositions and optical properties were explored by scanning electron microscopy, energy dispersive spectroscopy and spectrophotometer UV-VIS-NIR, respectively. X-ray diffraction and Raman analysis confirm that the sulfurization process leads to the formation of single CCTS phase. Optical results show high absorption coefficients of 105 cm-1 in the visible range with direct optical band-gap in the range 1.40-1.43 eV. In addition, the p-type conductivity of CCTS thin films was confirmed by hot probe method. The degradation of methylene blue in the presence of post-sulfurized samples was found in the range of 62-73%. Optical and Photocatalytic properties proves that post-sulfurized samples are suitable for application in photovoltaic and photocatalysis.

An Easily Constructed and Inexpensive Tool to Evaluate the Seebeck Coefficient

Genuinely inexpensive and easily constructable setup designs are important and encouraging for the new starters/students to build and use them as material testing tools during the initial stage of their research. A low-cost do it yourself (DIY) apparatus is designed and built for the accurate and reliable measurement of the Seebeck coefficient. The tool is portable and very easy to operate. It contains a miniaturized electrode designed for hot probe that helps data acquisition in a short time and avoids extra heat consumption and losses that occur in case of bulk probes. The tool also provides an easy sample loading/unloading facility; samples can be loaded/unloaded in just few seconds. It has been checked for its reliable working by measuring the Seebeck coefficient of some standard samples, giving reproducible measured data that are comparable to the literature values. The tool is suitable for the room temperature measurement but it is also demonstrated for temperature-dependent measurements up to 120 °C. As compared to most of the reported setups, the present design is simpler and can be built with commonly available raw materials. The tool is proposed as a simple, low-cost DIY testing unit for the thermoelectric materials.

Cost-effective SnS heterojunction solar cells synthesized by spray pyrolysis

The present study reports, synthesis and fabrication of SnS/n-Si (100) heterojunction solar cell by a cost-effective spray pyrolysis technique. XRD peaks resemble orthorhombic SnS. XRD and SEM study reveals crystal/grain size as 15 and 26.4 nm, respectively. The SnS surface is closely packed, and composition of Sn and S element weight% found to be 96.58 and 3.42, respectively, and hot probe method confirms intrinsic p-type conductivity due to excesses Tin in films. Raman spectral analysis confirms the SnS phase along with Sn2S3 and SnS2. Isochronal and isothermal studies show that film sheet resistivity attains lowest value of 1.7248 × 10−2 Ωcm when annealed at 200 °C for 15 min. From M-S contact studies, estimated reverse saturation current density, ideality factor, knee voltage, barrier potential, and disorder energy are found to be 3.0563 × 10−10 A cm−2, 1.5225, 0.158 V, 0.7669 eV, and 0.0864 eV. Solar cell exhibits a typical rectifying diode behavior and its series resistance decreases from 41.44 to 16.66 kΩ as film thickness increases from 37 to 63 nm under illumination of 206 mW cm−2.

New salicylaldehyde azine esters: Structural, aggregation induced fluorescence, electrochemical and theoretical studies

The establishment of high-tech products relying on organic optoelectronics is focused towards latest strategies for improving the processability and performance. In the present study, two esters of salicylaldehyde azine SAE-F and SAE-NF were synthesized and their structural characterization were performed using FT-IR, 1H and 13C NMR, UV–visible spectroscopy, mass spectrometry and single crystal-XRD technique. The bathochromic shift observed in luminescence measurements from solution to aggregate/solid state, solvent based fluorescence studies, SEM and DLS measurements confirmed the fluorescence emission from the SAE-F aggregates. The DSC data indicated the phase transitions, and the TGA measurements confirmed the thermal stability of SAE-F to withstand temperatures up to 225 °C. The morphological characterization revealed formation of homogeneous pin-hole free uniform films of SAEF. Cyclic voltammetry was used to estimate the HOMO and LUMO energy levels which were found to be −5.46 eV and −3.05 eV respectively with a band gap of 2.41 eV. The p-type semi-conductivity of SAE-F was established using hot probe technique. The dielectric measurements were carried out to measure dielectric constant and ac conductivity at different frequency ranges. The electronic data obtained based on Density Functional Theory calculations were in conformity with the experimental results. Successful fabrication of a diode and the recorded current-voltage characteristics clearly advocated SAE-F to be an excellent candidate for electro-optical devices.

Impact of Tin concentration in ITO films on Optoelectronic sensor performance

In viewing the opportunity to enhance Photovoltaic application, nine samples having different concentrations (5%, to 70%) were synthesized by sol gel Acrylamide route. XRD study indicates the entire films exhibited single phase with bixbyte structure for all films. EDXA studies confirm the existence SnO2 enclosures in the entire samples. Atomic force micrographs of ITO films conclude that the grain size decreases with increase of tin concentration. Hot probe measurements reinforce the optimum concentration of tin (10%) for its transport properties, their optoelectronic application of DSSC. This paper focuses on the DSSC performance. In this work ITO films and their gas sensing characteristics are studied and their results are reported. ITO based H2S sensor with 70% tin concentration exhibited maximum sensitivity at 100 °C with higher recovery time than the response times. After a long time, ITO films with different concentrations of tin (450 °C) return to the original state.

Structural, morphological and electrical properties of the Al/p-Cu2FeSnS4 thin film Schottky diode grown by two method

This work highlights some physical properties of Al/p-Cu2FeSnS4 Schottky diode fabricated by a two-stage method. Foremost, the Cu2FeSnS4 (CFTS) thin film was grown using thermal evaporation method onto heated Mo substrate temperature at 150 °C. After that, the as-deposited CFTS sample was annealed in a sulfur atmosphere at 400 °C for 30 min. Structural and morphological characterization were carried out by X-Ray diffraction, Raman scattering and scanning electron microscopy, whereas electrical study of Al/p-Cu2FeSnS4 junction was performed by using the current-voltage (I-V) measurement. Structural study revealed the presence of stannite CFTS phase and other peaks like Mo and MoS2. The hot probe method indicates that CFTS thin film exhibit p-conductivity type, also the film thickness was around 500 nm. The I-V characteristics showed that a Schottky contact was obtained between Aluminum and p-Cu2FeSnS4 absorber layer. The saturation current, the ideality factor and series resistance were determined from I-V experimental data. These parameters show important electrical properties such as a low series resistance and an ideality factor between 1 and 2.

Al doping for bipolarity induction in transparent conducting CuInO2 and its application in diode fabrication

Al doping is used in transparent conducting CuInO2 (CIO:Al) thin films for producing bipolar electrical conductivity. The doped thin films of electrical conductivity ~2 to 4 S/cm and mobility 100 to 101 V/cm2 are deposited by oxygen plasma assisted reactive evaporation technique. The change in conductivity from n-to p-type with the variation in doping atomic percentage is confirmed by multiple techniques like hot probe, hall and Seebeck measurements. The as deposited amorphous films are found to assume 3R poly type delafossite structure after post air annealing at 673 K. The suitability of the doped films in transparent device fabrication is verified by construction and characterization of a diode with configuration FTO/n-CIO:Sn/p-CIO:Al/Ag.

Isotype Heterojunction Solar Cells Using n-Type Sb2Se3 Thin Films

The carrier-type of the emerging photovoltaic Sb2Se3 was evaluated for both thin films and bulk crystals via a range of complementary techniques. X-ray photoelectron spectroscopy (XPS), hot probe, Hall effect, and surface photovoltage spectroscopy showed films and crystals synthesized from the Sb2Se3 granulate material to be n-type with chlorine identified as an unintentional n-type dopant via secondary ion mass spectrometry analysis. The validity of chlorine as a dopant was confirmed by the synthesis of intrinsic crystals from metallic precursors and subsequent deliberate n-type doping by the addition of MgCl2. Chlorine was also shown to be a substitutional n-type shallow dopant by density functional theory calculations. TiO2/Sb2Se3 n–n isotype heterojunction solar cells with 7.3% efficiency are subsequently demonstrated, with band alignment analyzed via XPS.

One-pot green synthesis of copper sulfide (I) thin films with p-type conductivity

In this work we describe a novel and eco-friendly, low temperature synthesis of copper sulfide (I) Cu2S thin films. Chemical bath deposition was successfully applied for the Cu2S films deposition from acidic aqueous solutions of sodium thiosulfate Na2S2O3. The characterization of the prepared films was accomplished through elemental analysis, scanning electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, Raman and transmittance spectroscopy, and hot point probe method. The potential application in solar cells and photocatalysis was demonstrated by the measuring the optical properties and conductivity type of the Cu2S thin films.

Synthesis and Characterization of Next Generation Cu2ZnxFe1−xSnS4 (x = 0, 0.25, 0.5, 0.75 and 1) Compounds

In this paper, we investigate the effect of Zn/Fe ratio on the properties of Cu2ZnxFe1−xSnS4 (CZFTS) compounds. Multicomponent CZFTS powders were prepared by direct melting of the constituent elements taken in stoichiometric compositions. After that, CZFTS thin films were fabricated using a single source vacuum thermal evaporation method. After that, CZFTS thin films were annealed in sulfur atmosphere under nitrogen flow at 400°C for 30 min. Structural properties of CZFTS powders and thin films were studied by elemental composition measurement, x-ray diffraction (XRD) and Raman spectroscopy. Analysis of chemical compositions reveals that the synthesized CZFTS powders are close to the expected stoichiometry. XRD patterns and Raman spectra of CZFTS powders showed that only polycrystalline CZFTS phase is present and a possible transition phase from stannite to kesterite structure had occurred by reducing Fe content. Using XRD data, the crystal parameters of CZFTS powders were estimated. Structural properties of CZFTS thin films indicate an enhancement of crystallinity after annealing. Some microstructural parameters of the prepared films were evaluated. However, morphological analysis of CZFTS crystals showed compact surfaces. Also, micrographs of CZFTS thin films indicate an improvement of crystallinity films followed by the increases of average roughness values after a sulfurization process. Moreover, hot probe method indicates that CZFTS ingots and prepared films exhibit an obvious p-type semiconductor.